Control of free piston type internal-combustion engines



EQ. .w

R. J. WELSH CONTROL 0F FREE PISTON TYPE Aug. 29, 1950 l Im'ERNAL-couusnon ENGINES Filed oct. 14; 1947 m w :o .M UMWIIHHQIIIIIl-lllllllo m L m3 o u E .Q

INVENT OR z ATTORNEYS ROBERT J. WELSH @S W Suv /NS Y Filed (krt- 14, 1947 Allg. 29, 1950 R, WELSH 2,520,294

CONTROL 0F FREE PISTON TYPE INTERNAL-COMBUSTION ENGINES f f2 Sheets-Sheet 2 INVENTOR ROBERT J. WELSH www ATTORNEYS enema Aug. 2s, 195o CONTROL F FREE PISTON TYPE IN- TERNALQCOMBUSTION ENGINES Robert James Welsh, Rugby, England, asslgnor to The English Electric Company Limited, London, England, a British company Application October 14, 1947, Serial No. 779,798 In Great Britain October 12, 1942 Section 1, Public Law 690, August 8, 1948 Patent expires October 12, 1962 5 Claims. (Cl. 12S-46) This invention relates to a free piston type internal combustion compressor-i. e. a device wherein a compressor piston is directly connected to or combined with an internal combustion engine piston instead of being driven thereby through connecting rods, cranks and crankshafts. There are usually two opposed engine pistons reciprocable towards and away from each other in one cylinder; the engine is usually one operating on a two-stroke compression-ignition cycle, some or all of the air from the compressor serving to scavenge and charge the engine cylinder. l

A device of this kind may be used as a gas generator to supply motive fluid to another piece of apparatus such as a gas turbine, which may have as its working fluid either (I) solely air coming direct from the compressor or (II) solely the exhaust from the -engine cylinder (comprising the products of the combustion in the engine cylinder mixed with the scavenging air supplied to the engine by the compressor) or (III) a mixture of the engine exhaust with air coming direct from the compressor. The second of these three alternatives is most usual.

The stroke of the free piston of a gas generator as defined above is usually variable or at least the innermost point reached by the piston at the end of the compression of the charge in the engine cylinder (which may be called the inner dead centre) usually varies throughout operation. The pressure of the gas delivered by the gas generator has to vary during operation and more particularly where it is used to supply a prime mover such as a gas turbine the pressure has to vary throughout operation in accordance with variations in the load on the turbine.

According to the present invention the point in the piston stroke at which combustion is initiated during the movement of the free piston towards the inner dead centre is varied automatically substantially in accordance with the inner dead centre position reached by the piston at the end of the immediately preceding compression stroke. In the case of a gas generator of the .compression-ignition fuel-injection type, the

point in the stroke at which fuel injection commences is automatically variedpreferably by acting on the fuel injection pump arrangement to vary the point at which the operation of this pump commences.

In order to be better understood and readily carried into effect the invention is illustrated by way 'of example in the accompanying drawings of which Fig. 1"shows a typical free piston internal combustion engine compressor in elevation in part section, and Fig. 2 shows the mechanism according to the invention in section on a larger scale, this mechanism being indicated diagrammatically only in Fig. 1.

Referring first to Fig. 1, the free piston internal combustion engine compressor comprises a combustion cylinder |0I, a pair of compressor cylinders |02 and a pair of cushion cylinders |03 arranged in alignment with the combustioncylinder on either side of it. and a pair of free piston assemblies each consisting of an engine piston |04, a compressor piston |05 and a cushion piston |06 adapted to perform oppOsite reciprocating movements in the said cylinders, being linked by links |01 to a two-armed lever |08 pivoted on the engine body.

Air enters the compressor cylinders |02 through the air inlets ||4 and inlet valves ||2 and leaves them through outlet valves I3 and transfer ducts ||5. The compressed air enters the combustion cylinder |0| as soon as the scavenging ports |0|a are cleared by the one of the engine pistons |04, and the combustion products and scavenging air leaves the combustion cylinder |0| as soon as the exhaust ports |0|b are cleared by the other engine piston |04, via the exhaust pipe ||6 leading to a gas turbine (not shown).

Fuel is injected into the combustion cylinder |0| by a fuel pump I having the usual fuel control rack la, via the pipe the conventional fuel distributor H8 and pipes H9, leading to the fuel injector nozzles |09. The fuel pump is operated in a manner to be described more in detail with reference to Fig. 2, by a cam 2, which is angularly reciprocated by the free piston assemblies by being linked to them by means of the links |01, the two armed lever |08, the lever |20 and the link |2|.

The reciprocating movement of the free piston assemblies is transmitted also to the lever I2 through link I5 and any suitable link and lever mechanism coupled to the two armed lever |08 as diagrammatically indicated in Fig. 1.

In the particular mechanism shown in Fig. 2, the fuel injection pump is reciprocated by a follower bearing on the cam 2 (the fuel-cam) oscillated by a free piston unit, which cam itself may be angularly movable Withrespet"a to the means by which it is driven from the free piston, but preferably, as shown, the cam follower is angularly movable substantially around the centre of oscillation of the cam; a lever 3 for actuating the pump is mounted on the pivot 4 on one side of the cam 2 and carries a pivot pini on the other side of the cam shaft, the centre lines of the axes of the cam 2 and of the pivot pins l and 8 lying on a straight line when the fuel pump is not in motion. A pail` of equal cranks 8 and 'I carried respectively by the pivot pins l and 4 and having their free ends pivotally connected by a link 8 form a parallel link motion. 'I'he cam follower is a roller 8 mounted at such a point on link 8 that on movement of links 8. 'I and 8 relatively to lever 3 the motion of roller 8 is in an arc substantially about the axis o." cam 2, the roller 9 riding on the base circle of the cam 2. An extension 1a of crank 1 is connected to the servo-motor piston I8 reciprocable in cylinder I I and can thereby be rotated to different angular positions to move the roller l to various positions angularly around the fuel cam 2.

The lever I2 is linked at one end to the piston I8 and at the other end to a control piston I8 reciprocable in a control cylinder Il. An :Intermediate point on the lever I2 can be reciprocated. through link Ii, by the free piston unit during its stroke or at least during the last part of its compression stroke in the engine cylinder, thereby rocking the lever I2 about its pivotal point of attachment to the piston I8 to drive the control piston I3 inward. The latter then tends to force fiuid-usually.liquidout of the cylinder I l through a non-return valve I8 into an accumulator Il-which latter is shown as a cylinder I1 wherein liquid is stored underl pressure produced by the spring-loaded piston Ila but which can be any elastically deformable chamber such as one of bellows-like form or even a distensible elastic bag. The cylinder I4 has each end in communication with a storage reservoir I8 which keeps the cylinder I4 filled and it also has two ports Ila and Hb located relatively as shown. The piston I3 has an annular groove I3a. Normallyi. e. when the piston I8 is in its correct position having regard to the rinner dead'centre position reached by the free piston unit the piston I3 will end its in-stroke in such a position that its lower edge uncovers port Ida without uncovering port IIb whereby the liquid pumped into accumulator I I will return to cylinder I4 through port Ila and no motion of piston I8 takes place. If the free piston in-stroke increases the lower edge of the piston I3 will uncover port IIb and allow liquid to flow through this port to cylinder I4 from cylinder II whereby the biasing spring I8 can move piston I8 in the same direction as piston I3 until piston I8 is in a position corresponding to the new free-piston inner dead centre position. Similarly if the free-piston in-stroke decreases. the piston will not move inwards far enough for its lower edge to uncover port Ila and allow liquid to return to cylinder I4 from accumulator Il; hence when, on return movement of piston I3, the groove I3a puts port Ila in communication with port Hb liquid can flow from the accu- 1 mulator I'I into cylinder II and move piston I8- against the force of spring I8 and in the opposite direction from before-to bring this piston I8 again into a position corresponding to the free-piston inner dead centre. Since member I8 and piston I8 act differentially through lever I2 on piston I3 the latter can only make a normal stroke-and leave piston I8 at rest-so long as piston I8 is substantially in a position correspending to the free-piston dead centre-i. e. on each compression stroke of the free-piston unit the piston I8 will be in a position substantially corresponding to the inner dead centre position 4 reached at the end of the immediately preceding compression stroke.

The movement of piston I8 in response to an increase in the free-piston in-stroke will rock the links 8, 1 and 8 about the lever 3 in a sense to move the follower 8 around the cam 2 in the direction of motion of this cam, whereby the follower is engaged later by the projecting part of the cam and the initiation of fuel injection is delayed. An opposite movement of piston I8 in response to a decrease in the in-stroke will move the follower around the cam in the opposite direction, to advance the initiation of fuel inJection.

As the free-piston unit reciprocates, the cam I oscillates'; as the unit approaches the inner dead centre the 'cam-at. a point dependent on the angular position to which the follower has been moved around the cam-drives the follower 8 thereby bodily moving the follower, the link moa tion and the lever 3 to actuate the fuel pump I.

This movement and hence the stroke of pump I is determined by the dimensions of the cam 2 and is substantially independent of the varying timing of the starting of the pump operation.

It will be understood that the foregoing is given merely as an example of one method of carrying out the invention and that any various alternative mechanical devices could be used.

What I claim as my invention and desire to secure by Letters Patent is:

1. A free piston internal combustion engine compressor comprising a combustion cylinder, and at least one compressor cylinder; at least one engine piston and at least one compressor piston, the said pistons being adapted to reciprocate together as a free -piston assembly in the said cylinders at a variable length of stroke, fuel supply means to said engine cylinder, timing means operated by the said reciprocating free piston assembly adapted to initiate the combustion of the fuel supplied to the said combustion cylinder, means responsive to the length of the engine compression stroke of the said free piston assembly, and automatic means operatively connecting the said combustion initiating means with the said stroke responsive means in a sense of varying the point on the compression stroke at which combustion is initiated substantially in accordance with the inner dead centre position reached by the free piston assembly at the end oi' the immediately preceding engine compression stroke.

2. A free piston internal combustion engine compressor as claimed in claim l operating on the compression-ignition principle including a fuel pump and fuel injector nozzle as the fuel supply means to the combustion cylinder, a, timing gear for said fuel pump as the timing means adapted to initiate the combustion of the fuel supplied to the combustion cylinder, and in which the said stroke responsive means control the said timing gear.

3. A free piston internal combustion engine compressor as claimed in claim 1 including following up means adapted to control periodically the position of said timing means for initiating the combustion of the fuel in accordance with the innerdead centre position reached by the free piston assembly and to move the said timing means in accordance with the variations in position of the said inner dead centre positions so as to alter thereby the timing of the subsequent initiation of combustion.

4. A free piston internal combustion engine I compressor operating on the compression ignition principle, comprising a combustion cylinder and at least one compressor cylinder, at least one engine piston and 'at least one compressor piston, the said pistons being adapted to reciprocate together as a free piston assembly in the said cylinders at a variable length of stroke, a fuel injection pump adapted to supply fuel to said engine-cylinder, timing means for initiating the combustion of the fuel including a cam oscillated by the reciprocating free piston assembly and a cam follower adapted to operate the said fuel injection pump, following-up means adapted to control periodically the position of said timing means in accordance with the inner dead centreposition reached by the free piston assembly and to move the said timing means in accordance with the variations in position of the said inner dead centre positions so as to alter thereby the of the subsequent initiation of combustion by varying the relative angular position of the said cam and the said follower, means responsive to the length oi' the engine compression stroke of the said free piston assembly, and automatic means operatively connecting thel said timing means with the said stroke responsive means in a sense of varying the pointI on the compression stroke at which combustion is initiated substantially in accordance with the inner dead centre position reached by the free piston assembly at the end of the immediately preceding engine compression stroke.

5. A free piston internal combustion engine compressor as claimed in claim 4 including as follow-up means a cylinder adapted to be connected to' fluid pressure, a piston adapted to movel vtrol the ow of fluid to and from the said cylinder.

ROBERT JAMES WELSH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PA'EN'IS Number Name Date 2,084,823 Pateras-Pescara June 22, 1937 2,132,083 Pateras-Pescara Oct. 4, 1938 2,182.063 Steiner Dec. 5, 1939 FOREIGN PATENTS Number Country Date 509,111 Great Britain of 1939 794,632 France of 1936 865,164 France of 1941 

